Scientists from MIT and other institutions have analyzed particles from the asteroid Ryugu, collected by the Japanese Aerospace Exploration Agency's (JAXA) Hayabusa2 mission and returned to Earth in 2020. The research indicates that Ryugu formed on the outskirts of the early solar system before migrating toward the asteroid belt, settling in an orbit between Earth and Mars.
The analysis focused on detecting signs of an ancient magnetic field that may have existed during Ryugu's formation. Findings suggest that if such a field was present, its strength would have been minimal, estimated at around 15 microtesla, compared to Earth's magnetic field of approximately 50 microtesla.
Despite its weakness, this magnetic field could have influenced the accumulation of primordial gas and dust, playing a crucial role in the formation of asteroids and potentially contributing to the development of giant planets like Jupiter and Neptune. This study, published in the journal AGU Advances, marks the first evidence of a weak magnetic field in the distal solar system.
Benjamin Weiss, a professor at MIT and co-author of the study, stated, 'We’re showing that everywhere we look now, there was some sort of magnetic field that was responsible for bringing mass to where the sun and planets were forming.' The research team included various experts from institutions such as Caltech, Harvard University, and Tsinghua University.
The solar system formed approximately 4.6 billion years ago from a dense cloud of interstellar gas and dust, which collapsed into a swirling disk. Most material formed the sun, while the remaining debris created a solar nebula of ionized gas. Interactions between the sun and this disk likely generated a magnetic field that influenced the accretion of matter to form planets and asteroids.
Previous assessments indicated a magnetic field existed within the inner solar system, extending to about 7 astronomical units (AU) from the sun. However, the extent of this field into the outer solar system remained uncertain due to a lack of samples.
The Hayabusa2 mission provided a unique opportunity to study samples from Ryugu, believed to have formed beyond 7 AU. The team utilized a magnetometer to analyze the samples, which were about a millimeter in size. Their analysis revealed no clear evidence of a preserved magnetic field within Ryugu, suggesting either the absence of a nebular field or a field too weak to be recorded in the asteroid's grains.
Additionally, the researchers revisited data from previously studied meteorites, particularly 'ungrouped carbonaceous chondrites,' which may have originated from the outer solar system. Their reanalysis indicated these samples might be older than initially thought, with one sample showing a positive field detection of about 5 microtesla, supporting the existence of a weak magnetic field in the outer solar system.
The findings imply that even a weak magnetic field can significantly impact planetary formation at greater distances from the sun. The research team plans to investigate further with samples from the asteroid Bennu, returned by NASA's OSIRIS-REx mission in September 2023.